The art of polyurethane foam manufacture, and specifically the continuous production of open cell flexible polyurethane foam, is well developed. The use of organic blowing agents such as chlorofluorocarbons and methylene chloride were adopted by the industry long prior to the determination that the uncontrolled release of these compounds into the atmosphere might have a deleterious effect on the environment.
In recent years, governmental regulations have been adopted to restrict, or even ban, the industrial use of these and other organic compounds, where the risk of environmental damage or health hazards is believed to be significant. For example, the use of methylene chloride, a relatively inexpensive auxiliary blowing agent for use in the manufacture of flexible polyurethane foam has been restricted in several states. Worldwide efforts have been undertaken to curtail the release of chlorofluorocarbons into the atmosphere, and their use in the manufacture of flexible polyurethane foam in the United States is to be eliminated entirely by the end of 1992.
It is well known that flexible polyurethane foam can be produced without the use of auxiliary organic blowing agents. Sufficient gases can be generated to cause the foam to form the desired cellular structure by increasing the water content and the amount of reactive isocyanate groups in the composition. However, a foam formulation comprising water as the sole blowing agent produces a high exotherm during the reaction which can lead to scorching, or even ignition, of the foam material in the interior of the block. The use of auxiliary blowing agents, in fact, serves to reduce the tendency for scorching. The heat required to vaporize the organic blowing agent reduces the maximum temperature of the exotherm; and any residual organic blowing agent retained in the interior of the foam block, not being flammable, would not support combustion.
In order to produce flexible polyurethane foam of acceptable quality having a cross-section of from about 72 inches to 94 inches in width and 30 inches to 50 inches high using water as the sole blowing agent, it has been found desirable to rapidly cool the interior of the freshly produced foam material by drawing an air stream through the open cell foam material after the reaction has produced a stable configuration. Various methods and apparatus for rapidly cooling the foam are known to the art and do not constitute a part of the present invention.
Examples of prior art methods and apparatus for rapidly cooling newly produced open celled flexible polyurethane foam are disclosed in the following patents: U.S. Pat. No. 3,061,885 issued Nov. 6, 1962; U.S. Pat. No. 3,890,414 issued Jun. 17, 1975; U.S. Pat. No. 4,537,912 issued Aug. 27, 1985; and allowed co-pending application Ser. No. 07/674,438 filed Mar. 22, 1991 (U.S. Pat. No. 5,128,379, issued Jul. 7, 1992).
As the air stream passes through the interior of the hot foam material and into the process air stream collection system, it removes and carries with it solid particulate matter, carbon dioxide produced by the reaction and volatile and vaporized organic constituents, including blowing agents if any were used. Under the current regulatory requirements of most jurisdictions, the heated process air stream cannot be released directly into the atmosphere.
The vaporized constituents can include small amounts of unreacted isocyanates, stabilizers, antioxidants, organic blowing agents such as chlorofluorocarbons, fluorocarbons, hydrochlorofluorocarbons, methylene chloride, acetone and 1,1,1-trichloroethane, as well as trace volatile impurities from raw materials.
Solid particulate matter drawn from the freshly produced foam can include solid chemical constituents such as butylated hydroxylated toluene ("BHT") (an antioxidant), as well as loose pieces of foam debris that cling to, or are only partially detached from the foam block when the protecting webs of paper or polymer film are stripped from the bottom, side surfaces and/or top of the foam block after it leaves the casting conveyor in order to provide air permeable surfaces. Although not harmful to the macro-environment, the bits and pieces of foam debris would create a local nuisance and maintenance problem if discharged into the atmosphere. Solid chemical constituents, such as BHT, can be eliminated by reformulating the composition of the raw materials used to produce the foam.
In allowed co-pending FWC U.S. patent application Ser. No. 07/702,413, filed May 20, 1991(U.S. Pat. No. 5,123,936, issued Jun. 20, 1992) a method and apparatus is disclosed for the downstream treatment of a process air stream from the rapid cooling of flexible polyurethane foam that employs a water spray of fine droplets and a water-wetted mechanical filtration system to reduce impurities.